As an electrophotographic image forming apparatus, a copier, a printer, a facsimile apparatus, a multi-functional peripheral thereof and the like have been widely used. By electrophotography, it is possible to easily form an image with favorable image quality. An image forming apparatus by such a method is provided with a fixing device, in which the fixing device heats a toner image that is formed on recording paper and fixes a fused toner onto the recording paper.
A fixing belt system fixing device has been well known. In the fixing belt system, an endless fixing belt is extended between a heating roller and a fixing roller. The heating roller incorporates a halogen heater and the like. In this belt system, a pressure roller is used, and the pressure roller pressurizes the fixing roller via the fixing belt. In a pressure-contact part between the pressure roller and the fixing belt, a nip portion is formed. When recording paper passes through the nip portion, a toner is fixed onto the recording paper.
The fixing belt moves and runs along a width direction of the fixing belt (also referred to as horizontal slide or meandering) in a state of being extended between the fixing roller and the heating roller. In a case where a pair of belt-deviation preventing members are provided on both ends of the heating roller, a center of the width direction of the fixing belt is easily brought close to a center of a shaft direction of the heating roller so that it is possible to prevent meandering of the belt. However, the fixing belt largely moves along the width direction and the fixing belt gets too close to one end of the heating roller, thereby causing a state where an end face of the fixing belt and the belt-deviation preventing member are brought into so-called surface contact with each other, so that the end face of the fixing belt is damaged or the like, which has been problematic.
Therefore, Japanese Laid-Open Patent Publication No. 2011-28040 discloses a method of making it difficult for a fixing belt to be damaged. As shown in FIG. 4A to FIG. 4C, in the fixing device described in the patent publication, a fixing belt 450 is extended between a heating roller 430 and a fixing roller 440, and a pair of belt-deviation preventing members 470 is provided on both ends of the heating roller 430.
The belt-deviation preventing member 470 is provided with a flange 472 that projects outside from an outer circumferential surface of the heating roller 430, and the flange 472 includes an annular curved surface 473. The annular curved surface 473 includes a wall surface part facing an end face of the fixing belt 450, and the wall surface part is curved toward a direction departing from the end face of the belt 450. This makes it possible to bring a state where the end face of the fixing belt 450 and the belt-deviation preventing member 470 are brought into almost so-called line contact with each other so as to make a contact range of the belt 450 and the member 470 small.
However, as shown in FIG. 4B, a deviation preventing member is not provided on each of both ends of the fixing roller 440. Thus, the fixing roller 440 is able to move freely in a shaft direction thereof. In a case where a moving direction of the fixing roller is consistent with a moving direction of the fixing belt that meanders, force for moving the fixing roller in the shaft direction and force for moving the fixing belt in the width direction get together, whereby the fixing belt 450 is brought into extreme contact with the belt-deviation preventing member 470, so that there has been a possibility to damage the fixing belt.